This function is used to read data into the specified streambuf until a
user-defined match condition function object, when applied to the data
contained in the streambuf, indicates a successful match. The call will
block until one of the following conditions is true:

The match condition function object returns a std::pair where the second
element evaluates to true.

An error occurred.

This operation is implemented in terms of zero or more calls to the stream's
read_some function. If the match condition function object already indicates
a match, the function returns immediately.

The stream from which the data is to be read. The type must support
the SyncReadStream concept.

b

A streambuf object into which the data will be read.

match_condition

The function object to be called to determine whether a match exists.
The signature of the function object must be:

pair<iterator,bool>match_condition(iteratorbegin,iteratorend);

where iterator represents
the type:

buffers_iterator<basic_streambuf<Allocator>::const_buffers_type>

The iterator parameters begin
and end define the
range of bytes to be scanned to determine whether there is a match.
The first member
of the return value is an iterator marking one-past-the-end of the
bytes that have been consumed by the match function. This iterator
is used to calculate the begin
parameter for any subsequent invocation of the match condition. The
second member of
the return value is true if a match has been found, false otherwise.

After a successful read_until operation, the streambuf may contain additional
data beyond that which matched the function object. An application will
typically leave that data in the streambuf for a subsequent

The default implementation of the is_match_condition
type trait evaluates to true for function pointers and function objects
with a result_type typedef.
It must be specialised for other user-defined function objects.